In fanfic, "pining" is when one character spends a significant portion of the story loving another character in their secret heart, but not saying anything, usually because they assume the other party isn't interested. Meanwhile, the other party is sometimes written as oblivious (sometimes to a ridiculous extent) to the pining character's feelings. (Often until they get hit by the clue bus.) Variations include both characters pining for each other while being oblivious and one character knowing all along.

In some pairings, one character is more likely to be cast as the one pining for the other.

Many, though not all, fanworks that use the pining trope end up with the pined-for party getting clued in, returning the piner's affection, and finding their way to a happy ending.

A fan in 2016 wrote:

listen, there is absolutely nothing that gets me going like mutual seemingly unrequited pining like? i live for both people losing their minds over the other person in bitter silence. savoring every single accidental brush of their fingers, elbows, thighs, every stray glance, memorizing every gesture or expression they catch while the other isn’t looking, all while being absolutely convinced that it’s one-sided only to finally!! finally find out it wasn’t in a triumphant moment of bliss after years and years of delicious, soul-rending, torturous, heart-wrenching pining. i literally don’t care about the fact that this trope is predictable af and always plays out the same way i will still go wild over it every single time like they’ll be doing the same reveal scene i have seen a million times and i’m still on the edge of my seat gasping “are they gonna kiss???” [1]

Tropes Involving Pining

While pining is a trope in and of itself, it is also highly likely to appear alongside, or as part of, certain ship-focused tropes. Some tropes which frequently center on or involve pining include:

Slow Burn: Many slow burn or slow build fanworks involve one or both halves of the pairing pining for each other as they find their way towards acting on their feelings.

Friends to Lovers: Similarly, many "friends to lovers" tropes involve pining when one or both halves of the couple aren't sure whether the other sees them as more than a friend.

Hanahaki Disease: The Hanahaki Disease trope requires unrequited love, and thus is almost certain to involve pining on the part of the victim.

Didn't Know They Were Dating: In some versions of this trope, one party may believe that they are already in a relationship while the other pines helplessly, sure that their feelings aren't returned. In other versions, the couple may be having what one (or both) thinks or pretends is casual, emotionally detached, sex, while the other party (or both parties) are secretly in love.

Pretend Couple: Fake dating fanworks almost always involve pining of some kind as one, or both, halves of the pairing carry out a pretend relationship while secretly wishing it were real.